New insights into the grapevine physiological ripening disorder berry shrivel with focus on anthocyanin biosynthesis

The physiological ripening disorder berry shrivel (BS) leads to high economic losses, in Austria especially with the red wine cultivar Zweigelt (Vitis vinifera L.). Grapes showing BS symptoms are low in quality, characterized by low sugar contents, high acidity, reduced anthocyanin biosynthesis and strong off flavors. Symptoms appear randomly between years, vineyard sites, and vines, which complicates basic as well as applied research. Due to this complexity the causing agents and processes leading to symptom development are still unclear. One prerequisite to understand this phenomenon would be to determine the time point of BS induction. Our research aimed to identify these early processes leading to BS symptoms. On a time scale basis we analyzed the biosynthesis of anthocyanins (LC-MS/MS; qPCR) in healthy and BS symptomatic berries. Reduced concentrations of delphinidin and cyanidin glycosidic forms were determined in BS berries, whereas caftaric acid, quercetin-3-O-glucuronide and (+)-catechin were increased at the same time. Results of qPCR analyses showed a reduced expression of VviLAR1, VviUFGT, VviMYBA1/2 and VviMYBPA1 at veraison and an increase in the expression level of VviDFR and VviLDOX. These data as well as parallel analysed sugar metabolism results places the induction of BS before veraison. The identification of the actual causes of BS is still pending, but our results provide a first step toward elucidation of inducing events and follow up symptom progression.